The prevalence of diabetes, which is characterized by hyperglycemia resulting from defects in insulin secretion and/or actions, is reaching epidemic levels globally (American Diabetes Association, Diabetes care 36 Suppl 1:S67-74 (2013)). The International Diabetes Federation (IDF) estimated that there are currently 382 million diabetic patients worldwide, with ˜46% remaining undiagnosed until they develop diabetic complications. Over 548 billion USD was spent on diabetes healthcare in 2013 (International Diabetes Federation, IDF Diabetes Atlas, 6th edition/2013 update (2013)). According to the latest epidemiological survey conducted in Mainland China, there are currently 113.9 million adults with diabetes and 493.4 million adults with prediabetes (Xu et al., JAMA 310:948-959 (2013)). The vast majority of cases of diabetes fall into two broad etiopathogenetic categories: type 1 diabetes (T1D), an autoimmune disease characterized with insulin deficiency due to the immune-mediated destruction of insulin-producing pancreatic β cells, and type 2 diabetes (T2D), a disease characterized by insulin resistance and often associated with obesity or older age (van Belle et al., Physiological reviews 91:79-118 (2011)). Although T1D accounts for only about 5-10% of the total cases of diabetes, it is one of the most common chronic diseases in children and adolescents and the most severe type of diabetes, leading to lifelong dependency on daily insulin injections and increased morbidity and mortality due to debilitated microvascular and macrovascular complications (Maahs et al., Endocrinology and metabolism clinics of North America 39:481-497 (2010)). Moreover, the incidence of T1D continues to increase worldwide at a rate of nearly 3% per year (Gan et al., Current problems in pediatric and adolescent health care 42:269-291 (2012)). Even in those diagnosed with T2D, it is demonstrated that approximately 10% of patients are positive for at least one of the islet autoantibodies, and this group is often referred to as “latent autoimmune diabetes in adults (LADA)” (Naik et al., The Journal of clinical endocrinology and metabolism 94:4635-4644 (2009)). These patients share many genetic and immunological similarities with T1D but also have the characteristics of T2D—adult age at onset and initial response to oral hypoglycemic agents; however, LADA patients tend to become insulin dependent and unresponsive to oral medications (Guglielmi et al., Diabetes/metabolism research and reviews 28 Suppl 2:40-46 (2012)).
Currently, the detection of autoantibodies against pancreatic β-cell autoantigens, such as insulin autoantibody (IAA), glutamic acid decarboxylase antibody (GADA), insulinoma-associated protein 2 autoantibody (IA-2A), and zinc transporter 8 antibody (ZnT8A), remains the only biomarkers for distinguishing autoimmune diabetes from T2D and detecting those high risk individuals (Lebastchi and Herold, Cold Spring Harb Perspect Med 2:a007708 (2012)). However, these autoantibodies are measured by either conventional immunofluorescence staining or with specific radioimmunoassays (Knip et al., Diabetes 54 Suppl 2:S125-136 (2005)), both of which are tedious and time-consuming. The radioimmunoassays have concerns of the health risks and disposal issues posed by the use of radioisotopes. Moreover, these autoantibodies from the children are rarely detectable before six months after birth (Ziegler et al., Diabetes 48:460-468 (1999)). The diagnostic sensitivity of single autoantibody measurement in T1D patients is as low as 59%-67% (Lebastchi and Herold, 2012). The other immunological assays, including the cellular immunoblot, T-cell proliferation assay, and ELISPOT assay can evaluate cellular immune responses in patients with autoimmune diabetes; however, the limitations of these assays are the requirements for relatively large numbers of peripheral blood mononuclear cell (PBMC) cultures and the need for fresh cells (Lebastchi and Herold, 2012).